1. Field of the Invention
The present invention relates generally to a plate for stack type heat exchangers and heat exchanger using such plates. In particular, the present invention relates to a plate for stack type heat exchangers and heat exchanger using such plates, which is capable of improving its performance of heat exchange by preventing the non-uniform flow distribution of refrigerant and increasing the turbulent flow effect of refrigerant, achieving its miniaturization and its optimal performance of heat exchange by designing the width of the plate and the arrangement of protrusions in accordance with an improved regularity, and improving its durability by enhancing the strength of attachment of its U-turn portion.
2. Description of the Related Technology
In general, a heat exchanger is a device in which an interior refrigerant passage is formed so that refrigerant exchanges heat with external air while being circulated through the refrigerant passage. The heat exchanger is employed in a variety of air conditioning apparatus. Particularly, in an air conditioning apparatus for automobiles, a stack type heat exchanger is mainly employed.
As depicted in FIGS. 15 to 17, a conventional stack type heat exchanger comprises of a plurality of flat tubes 90, a plurality of fins 94 and two end plates 95L, 95R.
The flat tubes 90 are stacked side by side. Each of the flat tubes 90 is formed by attaching a pair of one-tank plates 91 to each other. Each of one-tank plates 91 includes a pair of cup portions 911A, 911B, which are formed side by side on the upper portion of the one-tank plate 91 and the cup portions 911A, 911B have slots 912A, 912B respectively. A heat exchange portion 913 is formed under the cup portions to communicate with the cup portions, is provided with a plurality of small, round protrusions 915 internally projected through an embossing process, and is divided into two sub-portions by a central, longitudinal partition protrusion 917. A U-turn portion 919 is formed under the central, longitudinal partition protrusion 917 to connect the two sub-portions of the heat exchange portion 913 to each other, and is also provided with a plurality of small protrusions 915. A flange 916 is formed along the edge of the plate to have the same height as that of the small, round protrusions 915. When two one-tank plates 91 are attached to each other, a pair of pockets 93A, 93B and a U-shaped refrigerant passage are formed. The fins 94 are positioned between each pair of neighboring flat tubes 90. The end plates 95L, 95R are respectively situated at the side ends of the heat exchanger to reinforce the structure of the heat exchanger. Two cylindrical manifold portions 96L, 96R are projected from the front pocket 93A of the manifold tube 90L, 90R so as to be connected to a refrigerant inflow pipe(not shown) and a refrigerant outflow pipe(not shown), respectively.
In a conventional air conditioning apparatus employing the conventional heat exchanger as its evaporator, refrigerant enters one pocket(front pocket) 93A of the manifold tube 90L and flows into the neighboring both side front pockets 93A of the neighboring flat tubes 90 through the slots 912A of the front pockets 93A of the inlet-side tubes 90. Thereafter, the refrigerant flows to the rear pockets 93B of the inlet-side tubes 90 through a first group of U-shaped refrigerant passages of the flat tubes 90. While the refrigerant passes through the U-shaped refrigerant passages, the refrigerant exchanges heat with the exterior air. Subsequently, the refrigerant flows into the rear pocket 93B, second group of U-turn passages and front pockets 93A of the outlet-side tubes 90 through a process similar to the above-described inlet-side process. Next, the refrigerant in the pockets 93A of the outlet-side tubes 90 is discharged to a compressor through the cylindrical manifold portion 96R and the refrigerant outflow pipe. The refrigerant is evaporated in the process of heat exchange, and accordingly is supplied to the compressor in a gaseous state. A two-tank plate is similar to the one-tank plate in construction and operation except that two pairs of cup portions are respectively formed on the upper and lower end portions of the plate. Accordingly, for ease of explanation, only one-tank plate is described here.
The performance of an evaporator, which supplies cooled air into the interior of an automobile, depends upon the value of thermal conductivity by area. The performance is realized in a process in which the relatively cold refrigerant flowing through the flat tubes 90 exchanges heat with the relatively hot exterior air through the fins 94 stacked between the flat tubes 90. A heat source having a relatively high temperature is required to evaporate refrigerant, and the enlargement of a heat exchange area in contact with the fins 94 and the increase of thermal conductivity are required to improve the effect of the evaporation of refrigerant. In the case of a heat exchanger used in an air conditioning apparatus for automobiles, the high performance of heat exchange and the miniaturization of the heat exchanger are required to satisfy the requirements of the reduction of weight and noise, the increase of the amount of wind and the convenience of mounting, thus the heat exchange area of a heat exchange plate cannot be excessively enlarged.
Although a reduction in the height of the fins 94 and an increase in the density of the fins 94 are proposed to solve the above-mentioned problem, these proposals may rather decrease the performance of heat exchange due to difficulty in the drainage of condensed water, a pressure drop of exterior air and a reduction in the amount of wind.
Of the principal factors affecting the performance of heat exchange, the area of a refrigerant passage is influenced by the number, size, shape and arrangement of protrusions 915, and the intervals between protrusions. In the case of a heat exchanger having a relatively large capacity the influence of the arrangement of the protrusions 915 may be rather inconsiderable, but in the case of a compact heat exchanger comprised of flat plates each having a relatively small width the influence of the protrusions 915 is considerable. When the size of the protrusions is larger than the width of the plate by a certain ratio and the density of the protrusions is relatively small, flow resistance against the refrigerant is small but the performance of heat exchange is decreased due to the non-uniform flow distribution of refrigerant, the reduction of turbulent flow effect and the reduction of the amount of thermal contact with fins 94. When the size of the protrusions is large in comparison with the width of the plate and the density of protrusions 915 is large, the effect of the evaporation of refrigerant is decreased due to an increase in flow resistance against the refrigerant. In such cases, although a decrease in the size of protrusions can be taken into account, the decrease in the size of the protrusions is difficult to employ due to difficulty in forming a protrusion to be smaller than a certain minimum and weakness in attaching two plates to each other.
The plate 91 is generally formed of a clad brazing sheet. The plate 91 is comprised of a pair of cup portions 911A, 911B, a heat exchange portion 913 having a plurality of protrusions 915, a longitudinal partition protrusion 917 and a U-turn portion 919. Each flat tube 90 is formed by attaching two plates 91 to each other. The flat tube 90 has a pair of pockets 93A, 93B formed side by side by attaching a pair of cup portion 911A, 911B to another pair of cup portions 911A, 911B. While the refrigerant flows from the front pockets 93A to the rear pockets 93B, the refrigerant passes through the U-turn portion 919 and the flow direction of the refrigerant is reversed. In consequence, a relatively great flow pressure of the refrigerant is exerted on the U-turn portion 919 in comparison with the other portions. However, the U-turn portion of one plate 91 and the U-turn portion of the other plate 91 are attached to each other only by the attachment of the small, round protrusions 915 of the two plates 91 since the longitudinal partition protrusion 917 is not extended to the lower end of the plate 91, resulting in the weakness of attachment. Accordingly, there occurs a concern that attached small, round protrusions 915 may be easily separated from one another. When the small, round protrusions 915 are separated from one another, the high flow pressure of the refrigerant is not resisted by the small, round protrusions 915 but is concentrated on the flanges 916 of the plates 91 attached to each other and formed along the edges of the plates 91. As a result, the high flow pressure of the refrigerant cannot be resisted by the flanges 916 sufficiently, so that the flanges 916 are separated, thereby causing the leakage of the refrigerant.
The above-described phenomenon generated in the U-turn portions 919 is easily understood in FIGS. 22 to 25. FIGS. 22 to 25 are views showing the flow distributions of the refrigerant in a conventional evaporator formed of conventional heat exchange plates and mounted in a bottom mounting fashion, which were measured in 1997 using a CFD software called xe2x80x9cFluentxe2x80x9d.
A problem in the flow distribution of the refrigerant is that the flow of the refrigerant is concentrated on the outer portions of the plates 91. When the flow of the refrigerant is not distributed uniformly over the plates but concentrated on the outer portions of the plates, the performance of heat exchange of the heat exchanger is considerably decreased. In particular, a relatively high flow pressure of the refrigerant is exerted to the U-turn portions 919 and the longitudinal partition protrusions 917 are not extended on the lower ends of the plates 91, so that the flanges 916 beside the U-turn portions 919 of the plates 91 are caused to be under increased high flow pressure. Consequently, as shown in FIGS. 22 to 25, the flow of refrigerant is pushed to the inlet-side portion of the longitudinal partition protrusion 917 and the flange 916, so that the flow distribution of refrigerant is not uniform over the entire plate 91.
The cylindrical manifold portion 96L or 96R projected from one 93A of the two pockets of the flat tube 90 connected to the refrigerant inflow pipe or refrigerant outflow pipe is formed when a pair of manifold plates each having a semi-cylindrical manifold portion are attached to each other.
When a heat exchanger is mounted in an automobile air conditioning apparatus, there can be employed either a top mounting fashion, in which the heat exchanger is mounted to allow the pockets 93A, 93B of the heat exchanger to be situated on the top of the heat exchanger, or a bottom mounting fashion, in which the heat exchanger is mounted to allow the pockets 93A, 93B of the heat exchanger to be situated on the bottom of the heat exchanger. The characteristics of the evaporator, such as heat exchange capacity, are different, depending upon a mounting fashion, the number of tubes, the positions of the refrigerant inflow pipe and the refrigerant outflow pipe. In practice, these differences may affect the performance of an automobile air conditioning apparatus.
A 24-row type evaporator means an evaporator formed by stacking twenty four pairs of plates 91, that is, twenty four tubes 90. A 24-row type 4/7-7/4-pass evaporator means an evaporator, in which twenty four tubes 90 are stacked together and the twenty four tubes are arranged in the order of four pairs of plates 91, a pair of manifold plates 91 (i.e. a manifold tube 90L) to which the refrigerant inflow pipe is connected, seven pairs of plates 91, another seven pairs of plates 91, a pair of manifold plates 91 (i.e. a manifold tube 90R) to which the refrigerant outflow pipe is connected and four pairs of plates 91. Two reinforcing end plates 95L, 95R are situated at both ends of the evaporator, respectively. A blank plate 91C having a closed cup portion 912A is situated in the center of the evaporator, and serves as a baffle to prevent refrigerant from flowing into a neighboring plate. Therefore this blank plate 91C divides the fluid passage into a first group of U-turn passages(inflow side group) and second group of U-turn passages(outflow side group).
The following table 1 shows the performances of compact type evaporators with regard to top and bottom mounting fashions. In the case of a 13xe2x80x9413-pass heat exchanger, there is a 9% difference in performance between top and bottom mounting fashions. The performance data shown in the table 1 were measured using a calorimeter for evaporators.
In the above table, xc3x84Pa means the amount of air pressure drop and xc3x84Pr means the amount of refrigerant pressure drop.
The difference in performance is confirmed by the flow distributions of refrigerant. The flow distributions are appreciated by the distributions of temperature. The distributions of temperature, as shown in FIGS. 18 to 21, can be measured by photographs taken at a position 1 m away from the front of the evaporator using an experimental apparatus called xe2x80x9cAir Conditioner Test Standxe2x80x9d, which has the same structure as that of an actual automobile air conditioning apparatus and is used to aid the development of the parts of an air conditioning apparatus and a heat exchanger.
In the case of 4/7-7/4-pass evaporator, as can be referred by FIG. 19, a relatively more amount of refrigerant flows toward the blank plate rather than toward the end plate, so that the flow distribution of refrigerant is not uniform over the entire evaporator, thereby reducing the cooling performance. Additionally, the flow distributions of refrigerant are considerably different for top and bottom mounting fashions.
As indicated in FIGS. 20 and 21, in the case of 3/8-7/4-pass evaporator, the flow distributions of refrigerant are considerably different for top and bottom mounting fashions.
When the flow distribution of refrigerant is not uniform and the flow distributions of refrigerant are considerably different for top and bottom mounting fashions, a single evaporator cannot be selectively mounted in top and bottom mounting fashions. Accordingly, the evaporators should be manufactured separately according to the mounting fashions, so that the productivity of the evaporator is lowered and the manufacturing cost of the evaporator increases.
When the performance of heat exchange is reduced due to the non-uniform flow distribution of refrigerant, the cooling effect in the interior of an automobile is deteriorated, thereby causing a driver and passengers to feel hot.
The reason why the flow rate of refrigerant flowing toward the blank plate is greater than the flow rate of refrigerant flowing toward the end plate 95L is that a burr portion is not formed around the slot 912A of the cup portion 911A of the end plate-side plate 91 of two manifold plates 91 while a burr portion is formed around the slot 912A of the cup portion 911A of the blank plate-side manifold plate 91.
The burr portion serves to allow the plates 91 to be desirably attached to each other and to prevent the plates 91 from falling down while stacked plates are moved for a brazing process. On one hand, since the burr portion of the blank plate-side manifold plate 91 is inserted into the slot 912A of the neighboring blank plate-side plate 91 in the flow direction of the refrigerant while the refrigerant flows toward the blank plate 95, the refrigerant flows smoothly. On the other hand, since the burr portion of the neighboring end plate-side plate 91 is inserted into the slot 912A of the end plate-side manifold plate 91 in the opposite direction of the flow direction of the refrigerant while the refrigerant flows toward the end plate 95L, flow resistance by the burr portion is exerted on the refrigerant. Accordingly, a relatively small amount of refrigerant flows toward the end plate 95L.
As a result, the flow rate of refrigerant flowing toward the end plate 95L is less than the flow rate of refrigerant flowing toward the blank plate, so that a uniform flow distribution is not achieved over the entire evaporator. Due to the difference in flow distribution over the entire evaporator, the cooling performance is decreased and difference in flow distribution becomes great between top and bottom mounting fashions.
While, since semi-cylindrical manifold plates are formed by deep drawing of thin plates the expanded portion, particularly, the manifold portions 96 are vulnerable to outer force exerted thereon and, thus, are apt to be deformed due to bending moment from the inflow pipe or the outflow pipe.
Accordingly, the present invention has been made keeping in mind the above problems, and one aspect of the present invention is to provide a heat exchanger having a manifold plate structure, which is capable of improving its performance of heat exchange by increasing the flowability of refrigerant.
Another aspect of the present invention is to provide a heat exchanger having a manifold plate structure, which is capable of producing a substantially constant air temperature regardless of the amount of wind by achieving the uniform flow distribution of refrigerant, thereby allowing a driver and passengers to feel cool and comfortable.
Another aspect of the present invention is to provide a heat exchanger having a manifold plate structure, which is capable of achieving its miniaturization and its optimum performance of heat exchange by designing the width of the plate and the arrangement of small, round protrusions according to an improved regularity.
Another aspect of the present invention is to provide a heat exchanger having a manifold plate structure which can enhance its durability by improving the strength of the connection portion between the manifolds and the refrigerant inflow pipe or outflow pipe.
Still another aspect of the present invention provides a heat exchanger having a manifold plate structure. The heat exchanger comprises a first end plate and a second end plate, and a plurality of flat tubes, each of the first and second end plates is configured on a respective side end of the heat exchanger. The plurality of flat tubes are stacked together so that plates constituting the flat tubes are arranged in the order of the second end plate, a first plurality of pairs of plates, a first pair of manifold plates to which a refrigerant inflow pipe is connected, the first pair of manifold plates having a first manifold plate which is located at a side of the first end plate and second manifold plate which is located at a side of the second end plate, a second plurality of pairs of plates, a second pair of manifold plates to which a refrigerant outflow pipe is connected and a third plurality of pairs of plates configured adjacent to the first end plate. The first burr portion which is projected from an edge of an inlet-side slot of the first manifold plate to an outside is fixedly inserted into a first slot of a plate among the second plurality of pairs of plates adjacent to the first manifold plate. A second burr portion which is projected from an edge of a second slot of a plate among the first plurality of pairs of plates adjacent to the second manifold plate is fixedly inserted into an inlet-side slot of the second manifold plate. Each of the length and width of the first slot and the length and width of the inlet-side slot of the first manifold plate is less than the length and width of the inlet-side slot of the second manifold plate, respectively.
Yet another aspect of the present invention provides a heat exchanger having a manifold plate structure. The heat exchanger comprises a first and a second manifold plate. The first and second manifold plates allow a refrigerant communication between an outside of the heat exchanger and another plate, the manifold plates together forming a closed flat tube and each having a pair of cup portions. The first manifold plate has a first slot and the second manifold plate has a second slot. The edge of the first slot has a projected burr portion. The first slot is configured for insertion into a slot of a first adjacent plate that is configured to be connected to the first manifold plate. The length and width of the first slot are less than the length and width of the second slot, respectively.
In this aspect of the invention, the heat exchanger further comprises a second adjacent plate having a pair of cup portions. At least one of the cup portions has a third slot having a burr portion that is projected from the edge of the third slot, and the third slot is configured for insertion into the second slot through a respective cup portion. The first slot is about 15 mm long and about 9 mm wide, while the second slot is about 16.6 mm long and about 10.8 mm wide. In this aspect of the invention, the heat exchanger further comprises a heat exchange portion and a flange. The heat exchange portion communicates with the cup portions of the manifold plates, has a plurality of small protrusions, and is divided into two sub-portions by a central longitudinal partition protrusion. The flange has the same height as that of the small protrusions and is formed along the edge of the manifold plates. Several vertical protrusions are formed side by side on an inlet-side sub-portion of the heat exchange portion under the inlet-side cup portion of the cup portions, both side vertical protrusions being respectively horizontally extended to the longitudinal partition protrusion and to a neighboring portion of the flange.